876 Dr. R. D. Kleeman on the Effect of the 



That this expression is practically true we can see from 

 the following example. 



We choose hydrogen as the ideal gas and get the normal 

 volume ^ = 22*4452 litres, which is a little too great. The 

 volume of one gram-molecule o£ carbon dioxide at 0° C. and 

 1 atmosphere is v 2 = 22'2635 litres. 



Vq for carbon dioxide is equal to — . 



Consequently 1 — v ' — O0081, 



a = 0'0134, 6 = 0-0054, a-b =0*0080. 



From the equation (9) it ought to be possible by trial to 

 determine how a and b vary with temperature at constant 

 pressure, at least when that pressure is not too high, because 

 all the terms in the formula are measurable quantities. 



From these lines it is furthermore seen that a series of 

 the form (4) is identically the same as an equation of the 

 form (1), a and b being any function of the temperature. 

 It is evident that from a series in powers of P it ought to 

 be easy to determine by trial what kind of functions of the 

 temperature the coefficients are, thus getting the variation 

 of a and b by aid of equation (4) for even higher pressures, 

 at least inasmuch as the form of van der Waals' equation 

 is true. 



Furthermore, a series of the form (4) is more convenient 

 to use by determining the volume than the solution of the 

 cubic (1). 



XCIV. The Effect of \the Transition Layer of a Liquid on its 

 Surface Tension. By < R. D. Kleeman, D.Sc. } B.A* 



IT requires the expenditure of energy to produce an 

 increase in the area of surface of a liquid. The surface- 

 tension is therefore the work done, keeping the temperature 

 constant, in producing unit increase in the area of surface 

 of the liquid. Now this increase of surface may be pro- 

 duced in a variety of ways, since it follows from thermo- 

 dynamics that the work done during an isothermal process 

 between given limits is independent of the nature of the path 

 of the process. One way suggested by Laplace is to suppose 

 a slab of liquid cut into two parts by an imaginary plane, 

 and the parts then separated by an infinite distance from one 

 another. If W denote the total amount of work done during 



* Communicated by the Author. 



